Managing blockchain-based centralized ledger systems

ABSTRACT

Disclosed herein are methods, systems, and apparatus, including computer programs encoded on computer storage media, for managing blockchain-based centralized ledger systems. One of the methods includes: receiving timestamps and associated signatures from an independent trust time server associated with a trust time authority by a centralized ledger server in a centralized ledger system, storing the timestamps and the associated signatures in a centralized trust timestamp blockchain that stores trust timestamp information of the trust time server for the centralized ledger system that stores data in blockchains each including a plurality of blocks, receiving a timestamp request for a block of a blockchain from a ledger server associated with the blockchain by the centralized ledger server, and transmitting a timestamp and associated signature that is stored in the timestamp blockchain and corresponds to the timestamp request to the ledger server by the centralized ledger server.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of PCT Application No.PCT/CN2019/104062, filed on Sep. 2, 2019, which is hereby incorporatedby reference in its entirety.

TECHNICAL FIELD

This specification relates to managing blockchain-based centralizedledger systems.

BACKGROUND

A ledger is typically used to record a history of transactions, such aseconomic and financial activities in an organization. Applications withledger-like functionality, such as custom audit tables or audit trailscreated in relational databases, have been built to maintain an accuratehistory of applications' data. However, building such applications istime-consuming and prone to human error. Also, as the relationaldatabases are not inherently immutable, any changes to the data are hardto track and verify.

Distributed ledger systems (DLSs), which can also be referred to asconsensus networks, and/or blockchain networks, enable participatingentities to securely, and immutably store data. DLSs are commonlyreferred to as blockchain networks without referencing any particularuser case. Examples of types of blockchain networks can include publicblockchain networks, private blockchain networks, and consortiumblockchain networks. Blockchain networks perform a consensus process tovalidate each transaction before the transaction can be added to theblockchain networks, which can be time-consuming, ineffective, andcomplicated.

Therefore, it would be desirable to develop a ledger system that caneffectively and securely manage transactions while providingimmutability, reliability, trustworthiness, and verifiability of thetransactions.

SUMMARY

This specification describes technologies for managing blockchain-basedcentralized ledger systems. These technologies generally involve ablockchain-based centralized ledger system (e.g., a universal auditableledger service system) that adopts a data structure of a blockchain toleverage immutability, reliability, and trustworthiness of data storedon the blockchain. The centralized ledger system can obtain trusttimestamp information from a trust time server that is independent fromthe centralized ledger system (e.g., a third-party, globallyacknowledged time authority). The centralized ledger system can leveragethe established trust on the timestamp information provided by the trusttimer server and integrate the trust timestamp information into thecentralized ledger system for the data stored on the blockchain, whichcan further enhance credibility, auditability, and legality of thestored data.

These technologies described herein can help reduce costs of obtainingtrust timestamp information from the trust time server. For example, thedescribed technologies can provide a cost-effective trust timestampservice for a large number of blocks in multiple blockchains maintainedby the centralized ledger system.

This specification also provides one or more non-transitorycomputer-readable storage media coupled to one or more processors andhaving instructions stored thereon which, when executed by the one ormore processors, cause the one or more processors to perform operationsin accordance with embodiments of the methods provided herein.

This specification further provides a system for implementing themethods provided herein. The system includes one or more processors, anda computer-readable storage medium coupled to the one or more processorshaving instructions stored thereon which, when executed by the one ormore processors, cause the one or more processors to perform operationsin accordance with embodiments of the methods provided herein.

It is appreciated that methods in accordance with this specification mayinclude any combination of the aspects and features described herein.That is, methods in accordance with this specification are not limitedto the combinations of aspects and features specifically describedherein, but also include any combination of the aspects and featuresprovided.

The details of one or more embodiments of this specification are setforth in the accompanying drawings and the description below. Otherfeatures and advantages of this specification will be apparent from thedescription and drawings, and from the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating an example of an environment that canbe used to execute embodiments of this specification.

FIG. 2 is a diagram illustrating an example of an architecture inaccordance with embodiments of this specification.

FIG. 3 is a diagram illustrating an example of an environmentimplementing trust timestamp services in a blockchain-based centralizedledger system in accordance with embodiments of this specification.

FIG. 4A is a diagram illustrating an example of a blockchain-basedcentralized ledger system for implementing a trust timestamp service ina single ledger server associated with a single client in accordancewith embodiments of this specification.

FIG. 4B is a diagram illustrating an example of a blockchain-basedcentralized ledger system for providing a trust timestamp service tomultiple clients by a joint ledger server in accordance with embodimentsof this specification.

FIG. 5 is a diagram illustrating an example of a process of maintaininga centralized trust timestamp blockchain in a blockchain-basedcentralized ledger system in accordance with embodiments of thisspecification.

FIG. 6 is a flowchart illustrating an example of a process that can beexecuted in accordance with embodiments of this specification.

FIG. 7 depicts examples of modules of an apparatus in accordance withembodiments of this specification.

Like reference numbers and designations in the various drawings indicatelike elements.

DETAILED DESCRIPTION

This specification describes technologies for managing blockchain-basedcentralized ledger systems. These technologies generally involve ablockchain-based centralized ledger system (e.g., a universal auditableledger service system) that adopts a data structure of a blockchain toleverage immutability, reliability, and trustworthiness of data storedon the blockchain. The centralized ledger system can obtain trusttimestamp information from a trust time server that is independent fromthe centralized ledger system (e.g., a third-party, globallyacknowledged time authority). The centralized ledger system can leveragethe established trust on the timestamp information provided by the trusttimer server and integrate the trust timestamp information into thecentralized ledger system for the data stored on the blockchain, whichcan further enhance credibility, auditability, and legality of thestored data.

These technologies described herein can help reduce costs of obtainingtrust timestamp information from the trust time server. For example, thedescribed technologies can provide a cost-effective trust timestampservice for a large number of blocks in multiple blockchains maintainedby the centralized ledger system.

The techniques described in this specification produce several technicaleffects. In some embodiments, the blockchain-based centralized ledgersystem can be a ledger system based on centralization, which can providea cryptographically verifiable state-independent data ledger storagewith time-critical auditing (with non-repudiation andtemper-resistance). In some embodiments, the blockchain-basedcentralized ledger system can provide ledger services based on a cloudplatform featuring centralized endorsement with credibility andneutrality. The blockchain-based centralized ledger system can providehighly reliable and high-performance auditable streaming ledger servicesby leveraging both a blockchain system's high credibility and acentralized system's high performance and low latency for handlingvarious types of data and logs with auditing requirements, traceability,and tracking.

In some embodiments, the blockchain-based centralized ledger system caninclude a central trusted authority that provides transparent,immutable, and cryptographically verifiable data that are stored inblocks of a blockchain data structure. In some embodiments, the storeddata can be in a log format, including, for example, not only fortransaction logs but also other transaction data and block data. Due tothe existence of the central trusted authority, the blockchain-basedcentralized ledger system does not need to perform consensus processesto establish trust, which can result in significant time- andcost-saving. In some embodiments, the blockchain-based centralizedledger system can be more efficient compared to a typicalblockchain-based distributed or decentralized ledger system. In someembodiments, the blockchain-based centralized ledger system can providea cloud-based storage service with enhanced trust, efficiency, andstorage performance.

In some embodiments, the blockchain-based centralized ledger system canenhance

credibility, auditability, and legality of stored data on a blockchain.For example, the centralized ledger system can interface with a trusttime server and provide trust timestamp information of the trust timeserver to clients of the blockchain-based centralized ledger system. Thetrust time server is independent from the centralized ledger system. Thetrust time server can be associated with a third-party trust timeauthority that provides accurate time services and can be acknowledgedor trusted, for example, globally, by the public, auditing entities(such as companies, institutions, or organizations), and/or legalentities (such as courts or governments). As the trustworthiness of thetimestamp information provided by the trust time server is acknowledged,integrating the timestamp information of the trust time server into thecentralized ledger system for the data stored on the blockchain canfurther enhance credibility, auditability, and legality of the datastored in the centralized ledger system.

In some embodiments, the blockchain-based centralized ledger systemfeatures respective rights of parties or participants of theblockchain-based centralized ledger system. For example, a client of theblockchain-based centralized ledger system can have a right of providinga signature for storing transaction data on a blockchain in thecentralized ledger system such that the client cannot repudiate thetransaction data. In some embodiments, the centralized ledger system hasa right of providing a signature for acknowledging the storage of thetransaction data such that the centralized ledger system cannot denystoring the transaction data. In some embodiments, a trust time serverhas a right of providing a signature for trust timestamp information forthe transaction data stored on the centralized ledger system such thatthe trust time server cannot deny the trust timestamp information. Insome embodiments, the three respective rights of the three parties (theclient, the ledger system, and the trust time server) are independentfrom each other, which can further enhance creditability andauditability of the transaction data stored in the centralized ledgersystem.

In some embodiments, the blockchain-based centralized ledger system canprovide enhanced orderliness and authenticity of transaction data storedon the blockchain. For example, the blockchain-based centralized ledgersystem can transmit trust timestamp requests for transaction data storedon a blockchain to the trust time server, and the trust time server canprovide trust timestamp information such as timestamps and associatedsignatures, for example, to authenticate or endorse the time of thetransaction data stored on a blockchain. The centralized ledger systemcan store the trust timestamp information, e.g., as transactions, in theblockchain. The trust timestamp information can be used to verifyorderliness and authenticity of the transaction data stored on theblockchain, which in turn can provide enhanced creditability,auditability and legality of the transaction data stored on theblockchain.

In some embodiments, the blockchain-based centralized ledger system canhelp reduce costs of obtaining trust timestamp information from thetrust time server. For example, the blockchain-based centralized ledgersystem can provide a cost-effective trust timestamp service for a largenumber of blocks in multiple blockchains maintained by the centralizedledger system. The trust time server charges the centralized ledgersystem for providing trust timestamp information to each timestamprequest, and thus the large number of timestamp requests can incur highcost on the centralized ledger system and clients. In some embodiments,the centralized ledger system can maintain a centralized trust timestampblockchain by transmitting (e.g., periodically) server timestamprequests to the trust time server and storing a series of trusttimestamps and associated signatures of the trust time server in aseries of timestamp blocks. The centralized ledger server can generatethe series of timestamp blocks each storing a respective trust timestampand associated signature of the trust time server. The timestamp blockscan be anchored or linked together in the centralized trust timestampblockchain. Two blocks can be anchored to each other by one of theblocks including information that uniquely identifies the other one ofthe blocks (e.g., a hash of the other one of the blocks), such that anychanges made to the other one of the blocks can be detected by examiningthe information included in the one of the blocks. The centralized trusttimestamp blockchain can be used to provide timestamp services to theblockchains in the centralized ledger system, which can avoidtransmitting the large number of timestamp requests directly to thetrust time server. In such a way, the centralized ledger system canreduce the overall cost for obtaining trust timestamp information fromthe trust time server.

In some embodiments, the blockchain-based centralized ledger system canreduce the number of timestamp requests transmitted to the trust timeserver. For example, the centralized ledger system can include multipleledger servers each storing transaction data in a respective blockchain.Each ledger server can transmit (e.g., periodically) timestamp requestsfor blocks in the respective blockchain. Instead of directlytransmitting the timestamp requests from the multiple ledger servers tothe trust time server, the centralized ledger system can include acentralized ledger server in communication with the multiple ledgerservers. The centralized ledger server can transmit (e.g., periodically)server timestamp requests to the trust time server and maintain thecentralized trust timestamp blockchain. The centralized trust timestampblockchain can be used to provide timestamp services to multipleblockchains in the centralized ledger system. For example, when thecentralized ledger server receives a timestamp request for a block in ablockchain from a ledger server associated with the blockchain, thecentralized ledger server can transmit a most recent timestamp andassociated signature stored in the centralized trust timestampblockchain to the ledger server. In such a way, the centralized ledgersystem can greatly reduce the number of timestamp requests transmittedto the trust time server, thereby reducing the cost for obtaining trusttimestamps from the trust time server.

In some embodiments, the blockchain-based centralized ledger system canprovide enhanced orderliness and authenticity of transaction data storedon the blockchains. For example, a ledger server can store a timestampand associated signature of the centralized trust timestamp blockchainin a particular timestamped block in a blockchain associated with theledger server. Thus, any block preceding the particular timestampedblock in the blockchain can be determined to be generated before a timepoint represented by the timestamp. Moreover, the timestamp blocks inthe centralized trust timestamp blockchain are anchored or linkedtogether. Multiple timestamped blocks storing respective timestamps andassociated signatures of the centralized trust timestamp blockchain in ablockchain can be also anchored with each other according to thetimestamps. One or more non-timestamped blocks can exist betweenadjacent two of the timestamped blocks and store no timestamp andassociated signature from the trust time server. Thus, the centralizedtrust timestamp blockchain can guarantee that non-timestamped blocks inthe blockchain between adjacent two timestamped blocks associated withadjacent two particular timestamps of the centralized trust timestampblockchain are generated at time points between the adjacent twoparticular timestamps.

To provide further context for embodiments of this specification, and asintroduced above, distributed ledger systems (DLSs), which can also bereferred to as consensus networks (e.g., made up of peer-to-peer nodes),and blockchain networks, enable participating entities to securely, andimmutably conduct transactions, and store data. Although the termblockchain is generally associated with particular networks, and/or usecases, blockchain is used herein to generally refer to a DLS withoutreference to any particular use case.

A blockchain is a data structure that stores transactions in a way thatthe transactions are immutable. Thus, transactions recorded on ablockchain are reliable and trustworthy. A blockchain includes one ormore blocks. Each block in the chain is linked to a previous blockimmediately before it in the chain by including a hash of the previousblock. Each block also includes a local timestamp (e.g., provided by acomputing device that generates the block or a computing system thatmanages the blockchain), its own hash, and one or more transactions. Forexample, the block can include a block header and a block body. Theblock header can include the local timestamp, its own hash, and a hashof the previous block. The block body can include payload informationsuch as the one or more transactions (or transaction data). Thetransactions, which have already been verified by the nodes of theblockchain network, are hashed and encoded into a Merkle tree. A Merkletree is a data structure in which data at the leaf nodes of the tree ishashed, and all hashes in each branch of the tree are concatenated atthe root of the branch. This process continues up the tree to the rootof the entire tree, which stores a hash that is representative of alldata in the tree. A hash purporting to be of a transaction stored in thetree can be quickly verified by determining whether it is consistentwith the structure of the tree.

Whereas a blockchain is a decentralized or at least partiallydecentralized data structure for storing transactions, a blockchainnetwork is a network of computing nodes that manage, update, andmaintain one or more blockchains by broadcasting, verifying andvalidating transactions, etc. As introduced above, a blockchain networkcan be provided as a public blockchain network, a private blockchainnetwork, or a consortium blockchain network.

In general, a consortium blockchain network is private among theparticipating entities. In a consortium blockchain network, theconsensus process is controlled by an authorized set of nodes, which canbe referred to as consensus nodes, one or more consensus nodes beingoperated by a respective entity (e.g., a financial institution,insurance company). For example, a consortium of ten (10) entities(e.g., financial institutions, insurance companies) can operate aconsortium blockchain network, each of which operates at least one nodein the consortium blockchain network. In some examples, within aconsortium blockchain network, a global blockchain is provided as ablockchain that is replicated across all nodes. That is, all consensusnodes are in perfect state consensus with respect to the globalblockchain. To achieve consensus (e.g., agreement to the addition of ablock to a blockchain), a consensus protocol is implemented within theconsortium blockchain network. For example, the consortium blockchainnetwork can implement a practical Byzantine fault tolerance (PBFT)consensus, described in further detail below.

In some embodiments, a centralized ledger system can also adopt the datastructure of a blockchain to leverage immutability, reliability, andtrustworthiness of data stored on a blockchain. In some embodiments,such a centralized ledger system can be referred to as ablockchain-based centralized ledger system or a universal auditableledger service system. In some embodiments, the blockchain-basedcentralized ledger system can include a central trusted authority thatprovides transparent, immutable, and cryptographically verifiable datathat are stored in blocks of a blockchain data structure. The storeddata can be in a log format, including, for example, not only fortransaction logs but also other transaction data and block data. Due tothe existence of the central trusted authority, the blockchain-basedcentralized ledger system does not need to perform consensus processesto establish trust. In some embodiments, the blockchain-basedcentralized ledger system can be more efficient compared to a typicalblockchain-based distributed or decentralized ledger system. In someembodiments, the blockchain-based centralized ledger system can providea cloud-based storage service with enhanced trust, efficiency, andstorage performance.

In some embodiments, the centralized ledger system can be a node of ablockchain network. For example, the centralized ledger system can be anon-consensus node in the blockchain network and can provide highlyreliable and high-performance auditable streaming ledger services forthe consensus nodes or other non-consensus nodes in the blockchainnetwork, or entities outside of the blockchain network.

FIG. 1 is a diagram illustrating an example of an environment 100 thatcan be used to execute embodiments of this specification. In someexamples, the environment 100 enables entities to participate in aconsortium blockchain network 102. The environment 100 includescomputing devices 106, 108, and a network 110. In some examples, thenetwork 110 includes a local area network (LAN), wide area network(WAN), the Internet, or a combination thereof, and connects web sites,user devices (e.g., computing devices), and back-end systems. In someexamples, the network 110 can be accessed over a wired and/or a wirelesscommunications link. In some examples, the network 110 enablescommunication with, and within the consortium blockchain network 102. Ingeneral the network 110 represents one or more communication networks.In some cases, the computing devices 106, 108 can be nodes of a cloudcomputing system (not shown), or each computing device 106, 108 can be aseparate cloud computing system including a number of computersinterconnected by a network and functioning as a distributed processingsystem.

In the depicted example, the computing devices 106, 108 can each includeany appropriate computing system that enables participation as a node inthe consortium blockchain network 102. Examples of computing devicesinclude, without limitation, a server, a desktop computer, a laptopcomputer, a tablet computing device, and a smartphone. In some examples,the computing devices 106, 108 host one or more computer-implementedservices for interacting with the consortium blockchain network 102. Forexample, the computing device 106 can host computer-implemented servicesof a first entity (e.g., user A), such as a transaction managementsystem that the first entity uses to manage its transactions with one ormore other entities (e.g., other users). The computing device 108 canhost computer-implemented services of a second entity (e.g., user B),such as a transaction management system that the second entity uses tomanage its transactions with one or more other entities (e.g., otherusers). In the example of FIG. 1, the consortium blockchain network 102is represented as a peer-to-peer network of nodes, and the computingdevices 106, 108 provide nodes of the first entity, and second entityrespectively, which participate in the consortium blockchain network102.

FIG. 2 is a diagram illustrating an example of an architecture 200 inaccordance with embodiments of the specification. The example conceptualarchitecture 200 includes participant systems 202, 204, 206 thatcorrespond to Participant A, Participant B, and Participant C,respectively. Each participant (e.g., user, enterprise) participates ina blockchain network 212 provided as a peer-to-peer network includingmultiple nodes 214, at least some of which immutably record informationin a blockchain 216. Although a single blockchain 216 is schematicallydepicted within the blockchain network 212, multiple copies of theblockchain 216 are provided, and are maintained across the blockchainnetwork 212, as described in further detail herein.

In the depicted example, each participant system 202, 204, 206 isprovided by, or on behalf of Participant A, Participant B, andParticipant C, respectively, and functions as a respective node 214within the blockchain network. As used herein, a node generally refersto an individual system (e.g., computer, server) that is connected tothe blockchain network 212, and enables a respective participant toparticipate in the blockchain network. In the example of FIG. 2, aparticipant corresponds to each node 214. It is contemplated, however,that a participant can operate multiple nodes 214 within the blockchainnetwork 212, and/or multiple participants can share a node 214. In someexamples, the participant systems 202, 204, 206 communicate with, orthrough the blockchain network 212 using a protocol (e.g., hypertexttransfer protocol secure (HTTPS)), and/or using remote procedure calls(RPCs).

Nodes 214 can have varying degrees of participation within theblockchain network 212. For example, some nodes 214 can participate inthe consensus process (e.g., as miner nodes that add blocks to theblockchain 216), while other nodes 214 do not participate in theconsensus process. As another example, some nodes 214 store a completecopy of the blockchain 216, while other nodes 214 only store copies ofportions of the blockchain 216. For example, data access privileges canlimit the blockchain data that a respective participant stores withinits respective system. In the example of FIG. 2, the participant systems202, 204, and 206 store respective, complete copies 216′, 216″, and216′″ of the blockchain 216.

A blockchain (e.g., the blockchain 216 of FIG. 2) is made up of a chainof blocks, each block storing data. Examples of data include transactiondata representative of a transaction between two or more participants.While transactions are used herein by way of non-limiting example, it iscontemplated that any appropriate data can be stored in a blockchain(e.g., documents, images, videos, audio). Examples of a transaction caninclude, without limitation, exchanges of something of value (e.g.,assets, products, services, currency). The transaction data is immutablystored within the blockchain. That is, the transaction data cannot bechanged.

Before storing in a block, the transaction data is hashed. Hashing is aprocess of transforming the transaction data (provided as string data)into a fixed-length hash value (also provided as string data). It is notpossible to un-hash the hash value to obtain the transaction data.Hashing ensures that even a slight change in the transaction dataresults in a completely different hash value. Further, and as notedabove, the hash value is of fixed length. That is, no matter the size ofthe transaction data the length of the hash value is fixed. Hashingincludes processing the transaction data through a hash function togenerate the hash value. An example of a hash function includes, withoutlimitation, the secure hash algorithm (SHA)-256, which outputs 256-bithash values.

Transaction data of multiple transactions are hashed and stored in ablock. For example, hash values of two transactions are provided, andare themselves hashed to provide another hash. This process is repeateduntil, for all transactions to be stored in a block, a single hash valueis provided. This hash value is referred to as a Merkle root hash, andis stored in a header of the block. A change in any of the transactionswill result in change in its hash value, and ultimately, a change in theMerkle root hash.

Blocks are added to the blockchain through a consensus protocol.Multiple nodes within the blockchain network participate in theconsensus protocol, and perform work to have a block added to theblockchain. Such nodes are referred to as consensus nodes. PBFT,introduced above, is used as a non-limiting example of a consensusprotocol. The consensus nodes execute the consensus protocol to addtransactions to the blockchain, and update the overall state of theblockchain network.

In further detail, the consensus node generates a block header, hashesall of the transactions in the block, and combines the hash value inpairs to generate further hash values until a single hash value isprovided for all transactions in the block (the Merkle root hash). Thishash is added to the block header. The consensus node also determinesthe hash value of the most recent block in the blockchain (i.e., thelast block added to the blockchain). The consensus node also adds anonce value, and a timestamp to the block header.

In general, PBFT provides a practical Byzantine state machinereplication that tolerates Byzantine faults (e.g., malfunctioning nodes,malicious nodes). This is achieved in PBFT by assuming that faults willoccur (e.g., assuming the existence of independent node failures, and/ormanipulated messages sent by consensus nodes). In PBFT, the consensusnodes are provided in a sequence that includes a primary consensus node,and backup consensus nodes. The primary consensus node is periodicallychanged, Transactions are added to the blockchain by all consensus nodeswithin the blockchain network reaching an agreement as to the worldstate of the blockchain network. In this process, messages aretransmitted between consensus nodes, and each consensus nodes provesthat a message is received from a specified peer node, and verifies thatthe message was not modified during transmission.

In PBFT, the consensus protocol is provided in multiple phases with allconsensus nodes beginning in the same state. To begin, a client sends arequest to the primary consensus node to invoke a service operation(e.g., execute a transaction within the blockchain network). In responseto receiving the request, the primary consensus node multicasts therequest to the backup consensus nodes. The backup consensus nodesexecute the request, and each sends a reply to the client. The clientwaits until a threshold number of replies are received. In someexamples, the client waits for f+1 replies to be received, where f isthe maximum number of faulty consensus nodes that can be toleratedwithin the blockchain network. The final result is that a sufficientnumber of consensus nodes come to an agreement on the order of therecord that is to be added to the blockchain, and the record is eitheraccepted, or rejected.

In some blockchain networks, cryptography is implemented to maintainprivacy of transactions. For example, if two nodes want to keep atransaction private, such that other nodes in the blockchain networkcannot discern details of the transaction, the nodes can encrypt thetransaction data. An example of cryptography includes, withoutlimitation, symmetric encryption, and asymmetric encryption. Symmetricencryption refers to an encryption process that uses a single key forboth encryption (generating ciphertext from plaintext), and decryption(generating plaintext from ciphertext). In symmetric encryption, thesame key is available to multiple nodes, so each node can en-/de-crypttransaction data.

Asymmetric encryption uses keys pairs that each include a private key,and a public key, the private key being known only to a respective node,and the public key being known to any or all other nodes in theblockchain network. A node can use the public key of another node toencrypt data, and the encrypted data can be decrypted using other node'sprivate key. For example, and referring again to FIG. 2, Participant Acan use Participant B's public key to encrypt data, and send theencrypted data to Participant B. Participant B can use its private keyto decrypt the encrypted data (ciphertext) and extract the original data(plaintext). Messages encrypted with a node's public key can only bedecrypted using the node's private key.

Asymmetric encryption is used to provide digital signatures, whichenables participants in a transaction to confirm other participants inthe transaction, as well as the validity of the transaction. Forexample, a node can digitally sign a message, and another node canconfirm that the message was sent by the node based on the digitalsignature of Participant A. Digital signatures can also be used toensure that messages are not tampered with in transit. For example, andagain referencing FIG. 2, Participant A is to send a message toParticipant B. Participant A generates a hash of the message, and then,using its private key, encrypts the hash to provide a digital signatureas the encrypted hash. Participant A appends the digital signature tothe message, and sends the message with digital signature to ParticipantB. Participant B decrypts the digital signature using the public key ofParticipant A, and extracts the hash. Participant B hashes the messageand compares the hashes. If the hashes are same, Participant B canconfirm that the message was indeed from Participant A, and was nottampered with.

FIG. 3 is a diagram illustrating an example of an environment 300 inaccordance with embodiments of this specification. The environment 300implements trust timestamp services in a blockchain-based centralizedledger system 310. The blockchain-based centralized ledger system 310adopts a data structure of a blockchain to leverage immutability,reliability, and trustworthiness of data stored on the blockchain. Thecentralized ledger system 310 can also integrate trust timestampinformation from a trust time server 350 that is independent from thecentralized ledger system 310 for the data stored on the blockchain,which can greatly enhance credibility, auditability, and legality of thestored data.

In some embodiments, the centralized ledger system 310 can be a cloudcomputing system including one or more computers interconnected by anetwork. The centralized ledger system 310 can include any appropriatecomputing devices. Examples of computing devices include, withoutlimitation, a server, a desktop computer, a laptop computer, a tabletcomputing device, and a smartphone.

In some examples, the centralized ledger system 310 includes one or moreledger servers 320-1 to 320-n (collectively referred to herein as“320”). Each ledger server 320 can host one or more computer-implementedservices for interacting with at least one client, e.g., client 1 orclient m. The client can be an individual, a company, an organization, afinancial institution, an insurance company, or any other type ofentity. In some cases, a client can be associated with one or moreledger servers. In some cases, a ledger server can be associated withone or more clients.

The ledger server 320 can host a transaction management system toprovide a ledger service for a client, e.g., client 1 or client m, andthe client can use one or more associated devices, e.g., client device340-1 or 340-m (collectively referred to herein as “340”), to access thetransaction management system to use the ledger service. The clientdevice 340 can include any appropriate computing devices.

The ledger service provided by the ledger server 320 can enable a clientto store its data in a transparent, immutable, and cryptographicallyverifiable blockchain data structure, e.g., a blockchain. Each ledgerserver, e.g., 320-1 or 320-n, can maintain a respective blockchain,e.g., 322-1 to 322-n (collectively referred to herein as “322”). In someembodiments, each ledger server 320 can perform similar functions tothose of a blockchain network node (e.g., the computing device 106 or108 of FIG. 1 or the computing device 202, 204 or 206 of FIG. 2) in ablockchain network. For example, each ledger server 320 can generateblocks and add the blocks to the blockchain 322. In some embodiments,each ledger server 320 can function as a central trusted authority anddoes not need to perform consensus processes with other nodes (e.g.,other client devices or other leger servers) to establish trust. Forexample, each ledger server 320 can perform similar functions to thoseof a non-consensus node of a blockchain network. In some embodiments,each ledger server 320 can be the single node that creates and/ormanages the blockchain 322.

In some embodiments, each client can be associated with a respectiveblockchain. In some embodiments, one or more clients can be associatedwith a same blockchain. In some embodiments, a blockchain can beassociated with one or more clients.

In some examples, client 1 is an individual, a company, or anorganization. The client device 340-1 associated with client 1 caninteract with the ledger server 320-1 to obtain a ledger service of thecentralized ledger system 310. For example, the client device 340-1 canaccess the blockchain 322-1 to read and store transaction dataassociated with client 1 through the ledger server 320-1. The clientdevice 340-1 can include, for example, any suitable computer, module,server, or computing element programmed to perform methods describedherein. In some embodiments, the client device 340-1 can include a userdevice, such as, a personal computer, a smartphone, a tablet, or otherhandheld device.

In some examples, client m is an insurance company or a financialinstitution such as a bank that has a number of individual users. Theclient device 340-m associated with client m can interact with theledger server 320-m to provide a ledger service of the centralizedledger system 310 to the individual users of client m. For example, theclient device 340-m can access the blockchain 322-m to read and storetransaction data associated with client m through the ledger server320-m. In some cases, a user of client m can request a ledger service ofthe centralized ledger system 310 through the client device 340-m.

The data stored in a blockchain can be in a log format, including, forexample, not only for transaction logs but also other transaction dataand block data. Each blockchain stores data in a way that the data isimmutable and cannot be altered or deleted. Using cryptography canenable verification that there have been no unintended modification tothe stored data. Thus, data recorded on the blockchain are reliable andtrustworthy.

The blockchain can include one or more blocks. Each block in theblockchain is linked to a previous block immediately before it in thechain by including a hash of the previous block. Each block alsoincludes a local timestamp, its own hash, and one or more transactionsor transaction data. For example, the block can include a block headerand a block body. The block header can include the local timestamp, itsown hash, and a hash of the previous block. The block body can includepayload information such as the one or more transactions or transactiondata. The local timestamp indicates a time point or instance when theblock is generated and/or added to the blockchain. The local timestampcan be internally provided by the ledger server 320, the centralizedledger system 310, or a central trusted authority associated with thecentralized ledger system 310.

In some embodiments, the ledger server 320 sequentially receives aseries of transactions associated with a client and then stores thetransactions in blocks of a blockchain. In some embodiments, the ledgerserver 320 can receive one or more transactions, for example, from oneor more client devices 340. The received transactions can be stored in adata buffer. The ledger server 320 can generate a block to store thetransactions, for example, including transferee and transfer oraccounts, transaction amounts, or other types of information of thetransactions.

In some embodiments, the ledger server 320 can store the transactions ina stream, array, or another data structure (referred to as a transactionstorage stream). For example, the transactions can be sequentiallystored in the transaction storage stream according to time of occurrenceof the transactions. Each transaction can have a respective transactionidentifier in the transaction storage stream, for example, according toits time of occurrence. The ledger server 320 can generate blocks toinclude a number of hashes for the transactions. In some embodiments,the hashes for the transactions can be stored according to the time ofoccurrence of corresponding transactions, instead of according to valuesof the hashes. In some embodiments, the hashes for the transactions canbe hashes of the transactions or hashes of the respective transactionidentifiers of the transactions. A block can include a hash of aprevious block immediately before it such that the blocks are anchoredwith each other to form a blockchain (or a block storage stream). Insuch a way, the blocks do not store details of the transactions. Thedetails of the transactions can be stored in the transaction storagestream in the ledger server 320 or a separate repository in thecentralized ledger system 310.

The ledger server 320 can also provide trust timestamp services to aclient. In some embodiments, the ledger server 320 can request trusttimestamps from the trust time server 350 for data stored in the ledgerserver 320, which can enhance credibility, auditability, and legality ofthe stored data. The trust time server 350 is independent from thecentralized ledger system 310. The trust time server 350 can beassociated with a third-party trust time authority that providesaccurate (or true) time services and can be, for example, globally,acknowledged or trusted by the public, auditing entities (such ascompanies, institutions, or organizations), and/or legal entities (suchas courts or governments). Trust timestamp information provided by thetrust time server 350 can be acknowledged or considered as legalitywithout notarization and/or forensic identification. For example, thetrust time server 350 can be a UTC (Coordinated Universal Time)/GMT(Greenwich Mean Time) server providing UTC/GMT time services. The trusttime server 350 can also be a time server of a trust authority providingstandard times for a country or a region.

The centralized ledger system 310 can communicate with the trust timeserver 350 through a network, e.g., the network 110 of FIG. 1. Inresponse to receiving a timestamp request from a customer, e.g., theledger server 320, the trust time server 350 can generate a timestampindicating a time point when receiving the timestamp request. The trusttime server 350 can generate a signature to authenticate the timestampand the timestamp request (e.g., a textual or imaging copy of thetimestamp request). For example, the trust time server 350 can use itsprivate key to sign, thus cryptographically encrypting, the timestampand the timestamp request. The trust time server 350 can generate adigital timestamp certificate including the timestamp and the associatedsignature and transmit timestamp information including the timestampcertificate to the customer. The trust time server 350 can provide thetrust timestamp service with a cost, e.g., $ 1 per timestamp request.

In some embodiments, the ledger server 320 transmits to the trust timeserver 350 a timestamp request for authenticating a time of a block in ablockchain. The timestamp request can include information of the block,e.g., a hash of the block. The time server 350 can generate and transmittimestamp information including the timestamp and associated signaturefor the block or a hash of the timestamp and associated signature. Afterreceiving the timestamp information from the trust time server 350, theledger server 320 can store the timestamp information or a hash of thetimestamp information into a following block immediately subsequent tothe block in the blockchain. In some embodiment, the timestampinformation can be stored as a transaction in the following block. Ablock storing the timestamp information can be referred to be atimestamped block. The timestamped block can be a block that includesonly the timestamp information, or a block that also include othertransactions in addition to the timestamp information. Timestampedblocks in the blockchain can be anchored or linked to each other in theblockchain.

In some embodiment, the ledger server 320 can periodically transmittimestamp requests for to-be-timestamped blocks in a blockchain to thetrust time server 350 with a predetermined triggering time period. Forexample, the ledger server 320 can include a timer counting a time aftertransmitting a first timestamp request. When the timer counts thepredetermined triggering time period, the ledger server 320 can betriggered to transmit a second timestamp request immediately subsequentto the first timestamp request. The centralized ledger system 310 or theledger server 320 can provide timestamp services with different costscorresponding to different triggering time periods. The triggering timeperiod can be predetermined by a client (or a user) associated with theblockchain or the ledger server 320. For example, the client can choosea timestamp service corresponding to a respective cost and a respectivetriggering time period.

In some embodiments, the ledger server 320 may not transmit timestamprequests to the trust time server 350 periodically. For example, theledger server 320 may transmit timestamp requests on demand or based onthe number of the blocks generated by the ledger server 320. Forexample, the ledger server 320 may transmit a timestamp request of ablock upon receiving instructions from the client, or upon apredetermined number of blocks have been recently added to theblockchain 322.

In some embodiments, the ledger server 320 may generate blocksperiodically at a predetermined time period of block generation. Thepredetermined triggering time period can be the same or different fromthe time period of block generation. The predetermined triggering timeperiod can be longer than the time period of block generation so thatnot every block is being timestamped, for example, due to the cost ofobtaining the timestamp from the trust time server 350. In someembodiments, the ledger server 320 may not generate blocks periodically.For example, the ledger server 320 may generate blocks on demand orbased on the number of the transactions received by the ledger server320. For example, the ledger server 320 may generate a new block uponreceiving a predetermined number of transactions.

In some embodiment, the ledger server 320 can include one or moreapplication programming interfaces (APIs) that is configured tocommunicate with the trust time server 350. An API can include a set ofsubroutine definitions, communication protocols, and tools for buildingsoftware, and defines functionality provided by a program (module,library) and allows abstraction from exactly how this functionality isimplemented. Software components interact with each other through theAPIs. In some embodiment, the ledger server 320 can include one or moreAPIs that can implement functionalities of receiving a hash of ato-be-timestamped block as an input for a timestamp request,transmitting the timestamp request to the trust time server 350, andreceiving trust timestamp information, e.g., a digital timestampcertificate or a timestamp and associated signature, sent by the trusttime server 350.

The ledger server 320 can include one or more APIs that are configuredto communicate with a client device 340 associated with a client. Theone or more APIs can implement functionalities such as receiving arequest for a timestamp service from the client device 340, listingdifferent timestamp services with different costs and differenttriggering time periods, receiving a selection among the timestampservices from the client device 340, and transmitting or displaying acorresponding cost with a corresponding triggering time period to theclient device 340. In some embodiment, the one or more APIs can alsoimplement functionalities such as receiving a request for verifying orauditing transactions stored on a blockchain associated with the clientand transmitting a verification or audition result to the client device340. As discussed with further details in FIGS. 4A and 4B, the one ormore APIs can also implement other functionalities such as receivingtransactions or transaction data and client signatures from the clientdevice 340 and transmitting a ledger signature indicating acknowledgingthe receipt or storage of the transactions or transaction data and/orthe client signatures.

In some embodiments, the centralized ledger system 310 includes acentralized server 330. The centralized server 330 can be incommunication with the number of ledger servers 320 in the centralizedledger system 310. In some embodiments, the ledger servers 320communicates with the client devices 340 through the centralized server330. For example, the centralized server 330 can receive data from aclient device 340 and send the data to a ledger server 320 correspondingto (or assigned to) the client device 340.

In some embodiments, the centralized server 330 can maintain a standardtime server for the centralized ledger system 310 and can provideinternal timestamps (and/or associated signatures) to the ledger servers320. For example, when a ledger server 320 generates a new block, theledger server 320 can obtain an internal timestamp (and/or associatedsignature) from the centralized server 330 and store the internaltimestamp (and/or associated signature) in the new block.

In some embodiments, each of the ledger servers 320 communicates withthe trust time server 350 through the centralized server 330. Forexample, the ledger servers 320 can transmit original timestamp requeststo the centralized server 330 and the centralized server 330 cantransmit the original timestamp requests or centralized server timestamprequests associated with the timestamp requests to the trust time server350, e.g., through a centralized API in the centralized server 330. Thecentralized server 330 can provide trust timestamp information obtainedfrom the trust time server 350 to the ledger servers 320. In some otherembodiments, as described above, each of the ledger servers 320 cancommunicate with the trust time server 350 directly without thecentralized server 330.

FIG. 4A is a diagram illustrating an example of a blockchain-basedcentralized ledger system 400 for implementing a trust timestamp servicein a single ledger server associated with a single client in accordancewith embodiments of this specification. The blockchain-based centralizedledger system 400 can include a single ledger server 420 dedicated toprovide a ledger service to a single client associated with a clientdevice 410. The blockchain-based centralized ledger system 400 can be anexample of the centralized ledger system 310 of FIG. 3. For example, theledger server 420 can be an example of the ledger server 320-1 of FIG.3. The client device 410 can be an example of the client device 340-1 ofFIG. 3. The client uses the client device 410 to access the ledgerservice provided by the ledger server 420, in the blockchain-basedcentralized ledger system 400. The ledger server 420 can also provide atrust timestamp service to the client by communicating with a trust timeserver 430, which can be, for example, the trust time server 350 of FIG.3.

The ledger server 420 can provide the ledger service and the trusttimestamp service exclusively to the client. The ledger server 420 canstore transaction data associated with the client in a blockchainexclusively for the client and independent (or separate) from otherclients in the centralized ledger system 400. The ledger server 420 canrequest and store trust timestamp information exclusively for thetransaction data associated with the client stored in the blockchain inthe ledger server 420. The client can have an administrative right forstoring transactions in the blockchain. In some cases, the client canprovide to a third party a secondary ledger right that allows the thirdparty to store transactions in the blockchain associated with theclient.

In some embodiments, when a transaction (or transaction data) associatedwith the client is stored in the ledger server 420, the client can usethe client device 410 to transmit a client signature to the ledgerserver 420. The client signature can indicate that the clientacknowledges that the transaction has been completed and/or is to bestored in the ledger server 420. Thus, the client cannot repudiate thetransaction.

In some embodiments, after receiving and/or storing the transaction (orthe transaction data) in the ledger server 420 (e.g., in a blockchain),the ledger server 420 can transmit a ledger signature to the clientdevice 410. The ledger signature can indicate that the ledger server 420acknowledges the receipt and/or storage of the transaction. Thus, theledger server 420 cannot deny storing the transaction.

In some embodiments, the ledger server 420 can transmit to the trusttime server 430 a timestamp request for transactions that are associatedwith the client and stored in the ledger server 420. The trust timeserver 430 can provide a timestamp and associated signature for thetransactions to the ledger server 420. The timestamp signature caninclude information of the transactions. Thus, the trust time server 430cannot deny that its endorsement of time of the transactions and thetimestamps for the transactions are trustworthy.

In some embodiments, the three respective rights of the three parties(the client, the ledger server, and the trust time server) areindependent from each other, which can enhance creditability andauditability of the transaction data stored in the centralized ledgersystem.

FIG. 4B is a diagram illustrating an example of a blockchain-basedcentralized ledger system 450 for providing a trust timestamp service tomultiple clients by a joint ledger server in accordance with embodimentsof this specification. The blockchain-based centralized ledger system450 can include a single joint ledger server 470 for providing a ledgerservice to multiple clients, client 1 to client n. The blockchain-basedcentralized ledger system 450 can be another example of the centralizedledger system 310 of FIG. 3. For example, the joint ledger server 470can be an example of the ledger server 320 of FIG. 3. Each client,client 1 to client n, can be associated with a respective client device,460-1 to 460-n. In some embodiments, the client devices 460-1 to 460-ncan be examples of the client device 340-1 or 340-m of FIG. 3. Eachclient can use its respective client device 460 to access the ledgerservice provided by the ledger server 420, in the blockchain-basedcentralized ledger system 450. As an example, the clients can includemultiple financial institutions such as customer banks.

Each client can use its associated client device to store transactions(or transaction data) in a joint blockchain shared with other clients.Similar to FIG. 4A, each client can transmit a respective clientsignature to the ledger server 470 and the ledger server 470 can returna corresponding ledger signature to the client. The ledger server 470can transmit timestamp requests for the transactions stored in the jointblockchain to the trust time server 430 and receive and store timestampinformation for the transactions in the joint blockchain.

FIG. 5 shows an example of a process 500 of managing a centralized trusttimestamp blockchain in a blockchain-based centralized ledger system inaccordance with embodiments of this specification. The blockchain-basedcentralized ledger system can be an example of the centralized ledgersystem 310 of FIG. 3. The centralized ledger system can include acentralized ledger server 520, e.g., the centralized ledger server 330of FIG. 3. The centralized ledger server 520 can transmit (e.g.,periodically) server timestamp requests to a trust time server 510 andmaintain a centralized trust timestamp blockchain 530 by storing aseries of trust timestamps and associated signatures of the trust timeserver 510 received from the trust time server 510. The trust timeserver 510 is associated with a trust time authority and is independentfrom the centralized ledger system. The trust time server 510 can be,for example, the time server 350 of FIG. 3 or the time server 430 ofFIGS. 4A-4B. The centralized ledger server 520 can generate a series oftimestamp (TS) blocks, e.g., TS block m to TS block n+1, each storing arespective trust timestamp and associated signature of the trust timeserver 510. The timestamp blocks can be anchored or linked together inthe centralized trust timestamp blockchain 530 by, for example, storinga hash of a preceding timestamp block immediately before it in thecentralized trust timestamp blockchain 530.

The centralized trust timestamp blockchain 530 can be used to providetimestamp services to multiple blockchains in the centralized ledgersystem. When the centralized ledger server 520 receives a timestamprequest for a block in a blockchain from a ledger server associated withthe blockchain, the centralized ledger server 520 can transmit a mostrecent timestamp and associated signature stored in the centralizedtrust timestamp blockchain 530 to the ledger server.

As illustrated in FIG. 5, the centralized ledger server 520 can be incommunication with multiple ledger servers such as 540-i, 540-j(collectively referred to herein as “540”) that store transaction datain respective blockchains such as 542-i, 542-j (collectively referred toherein as “542”). Each ledger server 540 can be, for example, the ledgerserver 320 of FIG. 3, 420 of FIG. 4A, or 470 of FIG. 4B. Each blockchain542 can be, for example, the blockchain 322 of FIG. 3.

Each blockchain 542 can include multiple blocks. Each block has a blockidentifier and is sequentially added to the blockchain 542 according tothe block identifier. Each block in a blockchain is linked to a previousblock immediately before it in the chain by including a hash of theprevious block. Each block also includes an internal (or local)timestamp, its own hash, and one or more transactions or transactiondata. The internal timestamp indicates a time point when the block isgenerated and added to the blockchain. The internal timestamp can beinternally provided by the ledger server that generates the block, thecentralized ledger system or a central trusted authority associated withthe centralized ledger system. For example, as illustrated in FIG. 5,ledger server 540-i manages a blockchain 542-i that includes blocks i1to i5. Each of the blocks i1 to i5 has a block identifier i1 to i5 andis sequentially arranged and linked in order in the blockchain 542-iaccording to the block identifiers. Ledger server 540-j manages ablockchain 542-j that includes blocks j1 to j4. Each of the blocks j1 toj4 has a block identifier j1 to j4 and is sequentially arranged andlinked in order in the blockchain 542-j according to the blockidentifiers.

In the example 500, a ledger server 540 can transmit timestamp requestsfor blocks in its associated blockchain 542 to the centralized ledgerserver 520. For example, the ledger server 540 can periodically transmita timestamp request for a block in the blockchain 542 to the centralizedledger server 520 with a predetermined triggering time period. Thepredetermined triggering time period can be associated with acorresponding cost for a timestamp service of the centralized ledgersystem. The predetermined triggering time period can be predetermined bya client (or a user) associated with the blockchain 542 and the ledgerserver 540. Different ledger servers 540 can have different triggeringtime periods.

The predetermined triggering time period of the ledger server 540 can bethe same or different from a time period of block generation by theledger server 540. In some embodiments, the triggering time period canbe longer than the time period of block generation so that not everyblock is being timestamped, for example, due to the cost of obtainingthe timestamp from the trust time server 510. In some embodiments, theledger server 540 may not generate blocks periodically. For example, theledger server 540 may generate blocks on demand or based on the numberof the transactions received by the ledger server 540. For example, theledger server 540 may generate a new block upon receiving apredetermined number of transactions. In some embodiments, the ledgerserver 540 may not transmit timestamp requests to the trust time serverperiodically. For example, the ledger server 540 may transmit timestamprequests on demand or based on the number of the blocks generated by theledger server 540. For example, the ledger server 540 may transmit atimestamp request of a block upon receiving instructions from theclient, or upon a predetermined number of blocks have been recentlyadded to the blockchain.

The ledger server 540 can include a timer counting a time aftertransmitting a first timestamp request. When the timer counts to thepredetermined triggering time period, the ledger server 540 can betriggered to transmit a second timestamp request immediately subsequentto the first timestamp request among timestamp requests transmitted bythe ledger server 540 to the centralized ledger server 520. In somecases, the ledger server 540 generates blocks, e.g., according to apredetermined time period of block generation. In some embodiments, thepredetermined time period for block generation can be associated withthe predetermined triggering time period.

For example, as illustrated in FIG. 5, after transmitting a firsttimestamp request for the block i2 in the blockchain 542-i, the ledgerserver 540-i is triggered to transmit a second, immediately subsequenttimestamp request for block i5 after a predetermined triggering timeperiod for the ledger server 540-i. Similarly, after transmitting afirst timestamp request for the block j2 in the blockchain 542-j, theledger server 540-j is triggered to transmit a second, immediatelysubsequent timestamp request for block j4 after a predeterminedtriggering time period for the ledger server 540-j. The predeterminedtriggering time period for the ledger server 540-j can be different fromthe predetermined triggering time period for the ledger server 540-i.

In some embodiments, the centralized ledger server 520 is configured toperiodically transmit a centralized server timestamp request to thetrust time server 510 with a predetermined triggering time period. Thepredetermined triggering time period of the centralized ledger server520 can be shorter than any of the predetermined triggering time periodsof the ledger servers 540 in communication with the centralized ledgerserver 520 (or identical to the shortest predetermined triggering timeperiod of the ledger servers 540), such that the centralized ledgerserver 520 can accommodate timestamp requests from the ledger servers540.

In some embodiments, the server timestamp request is independent fromtimestamp requests from the ledger servers 540 and includes noinformation associated with blocks in the blockchains 542. Instead, theserver timestamp request includes only information of the centralizedtrust timestamp blockchain 530. In such a way, the centralized trusttimestamp blockchain530 maintained by the centralized ledger server 520can be independent from the ledger servers 540 and associatedblockchains 542 and can function as an independent time authority forproviding trust timestamp services to the ledger servers 540.

The server timestamp request can include information that uniqueidentifies at least one of a most recent timestamp block in thetimestamp blockchain 530, a most current timestamp block to be generatedin the timestamp blockchain 530, or the server timestamp request itself.In some cases, the server timestamp request includes an identifier ofthe server timestamp request among the server timestamp requeststransmitted to the trust time server 510. In some cases, the servertimestamp request includes a block identifier of a most currenttimestamp block to be generated in the timestamp blockchain 530. In somecases, the server timestamp request includes at least one of a blockidentifier or a hash of a most recent timestamp block generated in thetimestamp blockchain 530.

In response to receiving a server timestamp request from the centralizedledger server 520, the trust time server 510 can generate trusttimestamp information for the server timestamp request. The trusttimestamp information includes a trust timestamp indicating a time pointreceiving the server timestamp request and an associated signatureencrypting the trust timestamp and the server timestamp request.

After receiving the trust timestamp and associated signature from thetrust time server 510, the centralized ledger server 520 can generate anew timestamp block to store the trust timestamp and associatedsignature. The new timestamp block can also include a hash of apreceding timestamp block immediately before the new timestamp block inthe centralized timestamp blockchain 530, such that the new timestampblock is added to the centralized timestamp blockchain 530 andlinked/anchored to other preceding timestamp blocks in the centralizedtimestamp blockchain 530.

When receiving a timestamp request for a block in a blockchain 542 froma ledger server 540 associated with the blockchain 542, the centralizedledger server 520 can transmit a trust timestamp and associatedsignature that is stored in the timestamp blockchain 530 and correspondsto the timestamp request to the ledger server 540. The trust timestampand associated signature can be stored in a most recent timestamp blockgenerated in the timestamp blockchain when the timestamp request isreceived. In some embodiments, the centralized ledger server 520 cangenerate an internal (or local) timestamp for the timestamp blockstoring the trust timestamp and associated signature according to thecentralized trust timestamp blockchain530 and generate an internalsignature encrypting the internal timestamp and the timestamp block. Thecentralized ledger server 520 can also transmit the internal timestampand the internal signature to the ledger server 540, together with thetrust timestamp and associated signature obtained from the trust timeserver 510.

The ledger server 540 can then store the timestamp and associatedsignature as a transaction in the blockchain 542. In some cases, theblock to be timestamped can be the most recent block generated in theblockchain 542 when the timestamp request is transmitted. The timestamprequest can include a hash of the most recent generated block or otherinformation uniquely identifying the most recent generated block. Afterreceiving the corresponding timestamp and associated signature for themost recent generated block, the ledger server 540 can store thecorresponding timestamp and associated signature and/or a hash thereofas a transaction in a block immediately subsequent to the most recentgenerated block in the blockchain 542. The block immediately subsequentto the most recent generated block can also store the hash of the mostrecent generated block.

In some cases, the block to be timestamped can be the most current blockto be generated in the blockchain 542 when the timestamp request istransmitted. The timestamp request can include a hash of transactiondata to be stored in the most current block to be generated. Afterreceiving the corresponding timestamp and associated signature for themost recent generated block, the ledger server 540 can generate theblock storing the corresponding timestamp and associated signature as atransaction, together with the transaction data.

For example, as illustrated in FIG. 5, during a first predeterminedtriggering time period of the centralized ledger server 520 that isafter generating the timestamp block m+2 and before generating thetimestamp block m+3, the most recent generated timestamp block in thecentralized trust timestamp blockchain 530 is timestamp block m+2.During the first predetermined triggering time period, the centralizedledger server 520 receives a timestamp request for block i2 in theblockchain 542-i from the ledger server 540-i and a timestamp requestfor block j2 in the blockchain 542-j from the ledger server 540-j. Theblocks i2 and j2 can be the most current blocks to be generated in theblockchain 542-i and 542-j, respectively. The timestamp requests canrespectively include hashes of transaction data to be stored in theblock i2 and the block j2. The centralized ledger server 520 cantransmit the trust timestamp and associated signature stored in the mostrecent generated timestamp block m+2 to the ledger server 540-i and theledger server 540-j. The ledger server 540-i can generate the block i2that stores the trust timestamp and associated signature stored in thetimestamp block m+2 as a transaction and the transaction data for theblock i2. The ledger server 540-j can generate the block j2 that storesthe trust timestamp and associated signature stored in the timestampblock m+2 as a transaction and the transaction data for the block j2.

As illustrated in FIG. 5, during a second predetermined triggering timeperiod of the centralized ledger server 520 that is after generating thetimestamp block n and before generating the timestamp block n+1, themost recent generated timestamp block in the centralized trust timestampblockchain 530 is timestamp block n. During the second predeterminedtriggering time period, the centralized ledger server 520 receives atimestamp request for block i5 in the blockchain 542-i from the ledgerserver 540-i and a timestamp request for block j4 in the blockchain542-j from the ledger server 540-j. The blocks i5 and j4 can be the mostcurrent blocks to be generated in the blockchain 542-i and 542-j,respectively. The timestamp requests can respectively include hashes oftransaction data to be stored in the block i5 and the block j4. Thecentralized ledger server 520 can transmit the trust timestamp andassociated signature stored in the most recent generated timestamp blockn to the ledger server 540-i and the ledger server 540-j. The ledgerserver 540-i can generate the block i5 that stores the trust timestampand associated signature stored in the timestamp block n as atransaction and the transaction data for the block i5. The ledger server540-j can generate the block j4 that stores the trust timestamp andassociated signature stored in the timestamp block n as a transactionand the transaction data for the block j4.

As noted above, the predetermined triggering time period of thecentralized ledger server 520 can be shorter than any of thepredetermined triggering time periods of the ledger servers 540, suchthat the centralized trust timestamp blockchain 530 can accommodatetimestamp requests from the ledger servers 540. In some embodiments, thesecond predetermined triggering time period can be not immediatelysubsequent to the first predetermined triggering time period, and thetimestamp block n can be separated from the timestamp block m+2 by oneor more other timestamp blocks in the centralized trust timestampblockchain 530. The timestamp requests for block i2 and i5 can beimmediately subsequent among the timestamp requests transmitted from theledger server 540-i to the centralized ledger server 520. The timestamprequests for block j2 and j4 can be immediately subsequent among thetimestamp requests transmitted from the ledger server 540-j to thecentralized ledger server 520.

In some embodiments, the centralized timestamp blockchain 530 includestimestamp blocks each storing respective trust timestamp and associatedsignature of the trust time server 510 and the ledger servers 540 storetrust timestamps and associated signatures obtained from the centralizedtimestamp blockchain 530 for blocks of blockchains associated with theledger servers 540, orderliness and authenticity of transaction datastored in the blocks of the blockchains can be enhanced. For example, asillustrated in FIG. 5, for blockchain 542-i, block i2 includes a firsttrust timestamp from the timestamp block m+2, which can guarantee one ormore blocks preceding block i2, e.g., block i1, are generated before thefirst trust timestamp. Block i5 includes a second trust timestamp fromthe timestamp block n, which can guarantee one or more blocks precedingblock i5, e.g., blocks i1 to i4, are generated before the second trusttimestamp. Moreover, the timestamp block m+2 and timestamp block n aresequentially anchored together in the centralized timestamp blockchain530 and the blocks i2 to i5 are sequentially anchored together in theblockchain 542-i. Thus, the centralized timestamp blockchain 530 canguarantee that blocks between the blocks i2 and i5, i.e., blocks i3 andi4, are generated at time points between the first trust timestamp inthe block i2 and the second trust timestamp in the block i5.

Similarly, for blockchain 542-j, block j2 includes the first trusttimestamp from the timestamp block m+2, which can guarantee one or moreblocks preceding block j2, e.g., block j1, are generated before thefirst trust timestamp. Block j4 includes the second trust timestamp fromthe timestamp block n, which can guarantee one or more blocks precedingblock j4, e.g., blocks j1 to i3, are generated before the second trusttimestamp. Moreover, the timestamp block m+2 and timestamp block n aresequentially anchored together in the centralized timestamp blockchain530 and the blocks j2 to j4 are sequentially anchored together in theblockchain 542-j. Thus, the centralized timestamp blockchain 530 canguarantee that one or more blocks between the blocks j2 and j4, i.e.,block j3, are generated at time points between the first trust timestampin the block j2 and the second trust timestamp in the block j4.

FIG. 6 is a flowchart illustrating an example of a process 600 forimplementation of timestamp services that can be executed in accordancewith embodiments of this specification. For convenience, the process 600will be described as being performed by a system of one or morecomputers, located in one or more locations, and programmedappropriately in accordance with this specification. For example, acentralized ledger server in a blockchain-based centralized ledgersystem can perform the process 600. The centralized ledger system can bean example of the centralized ledger system 310 of FIG. 3. Thecentralized ledger server can be an example of the centralized ledgerserver 330 of FIG. 3 or 520 of FIG. 5.

At 602, timestamps and associated signatures are received from a trusttime server. The trust time server is associated with a trust timeauthority an independent from the centralized ledger system. The trusttime server can be, for example, the time server 350 of FIG. 3, the timeserver 430 of FIGS. 4A-4B, or the time server 510 of FIG. 5.

In some embodiments, the centralized ledger server is configured toperiodically transmit server timestamp requests to the trust time serverwith a predetermined triggering time period. Transmitting a servertimestamp request can be in response to determining that thepredetermined triggering time period has passed after a preceding servertimestamp request immediately before the server timestamp request istransmitted.

In some embodiments, the server timestamp request includes onlyinformation of the centralized trust timestamp blockchain. In such away, the centralized trust timestamp blockchain maintained by thecentralized ledger server can function as an independent time authorityfor providing trust timestamp services. In some cases, the servertimestamp request includes an identifier of the server timestamp requestamong the server timestamp requests transmitted to the trust timeserver. In some cases, the server timestamp request includes a blockidentifier of a most current timestamp block to be generated in thetimestamp blockchain. In some cases, the server timestamp requestincludes at least one of a block identifier or a hash of a most recenttimestamp block generated in the centralized trust timestamp blockchain.

In response to receiving a server timestamp request from the centralizedledger server, the trust time server can generate trust timestampinformation for the server timestamp request. The trust timestampinformation can include a trust timestamp indicating a time pointreceiving the centralized server timestamp request and an associatedsignature encrypting the trust timestamp and the centralized servertimestamp request. The trust time server can then transmit the trusttimestamp and associated signature to the centralized ledger server.

At 604, the timestamps and associated signatures of the trust timeserver are stored in a centralized trust timestamp blockchain. Thetimestamp blockchain can be, for example, the timestamp blockchain 530of FIG. 5. In response to receiving an individual timestamp andassociated signature from the trust time server, the centralized ledgerserver can generate a new timestamp block that stores the trusttimestamp and associated signature. The new timestamp block can alsoinclude a hash of a preceding timestamp block immediately before the newtimestamp block in the centralized timestamp blockchain, such that thenew timestamp block can be added to the centralized timestamp blockchainand linked/anchored to other preceding timestamp blocks in thecentralized timestamp blockchain. The centralized ledger server canmaintain the centralized timestamp blockchain by sequentially storetrust timestamps and associated signatures of the trust time server intimestamp blocks according to a chronological order of receiving thetimestamps and associated signatures from the trust time server. In someembodiments, the centralized ledger server can generate an internal (orlocal) timestamp for a new timestamp block and an internal (or local)signature encrypting the internal timestamp and the new timestamp block.

At 606, a first timestamp request for a first block of a firstblockchain is received from a first ledger server by the centralizedledger server. The centralized ledger system can include multiple ledgerservers maintaining multiple blockchains. The centralized ledger servercan be in communication with the multiple ledger servers. Each ledgerserver can be, for example, the ledger server 320 of FIG. 3, 420 of FIG.4A, 470 of FIG. 4B, or 540 of FIG. 5. Each blockchain can be theblockchain 322 of FIG. 3 or the blockchain 542 of FIG. 5. Each of theblockchains can include multiple blocks storing transaction data.

In some embodiments, a ledger server is configured to periodicallytransmit timestamp requests for blocks in its corresponding blockchainto the centralized ledger server at a predetermined triggering timeperiod. The predetermined triggering time period can be associated witha corresponding cost for a timestamp service of the centralized ledgersystem. The predetermined triggering time period can be predetermined bya client associated with the centralized ledger system. Different ledgerservers can have different predetermined triggering time period.

At 608, a first timestamp and associated signature that is stored in thetimestamp blockchain and corresponds to the first timestamp request istransmitted to the first ledger server by the centralized ledger server.The first timestamp and associated signature can be in a most recenttimestamp block generated in the centralized trust timestamp blockchainwhen the first timestamp request is received by the centralized ledgerserver. In some embodiments, the centralized ledger server can alsotransmit to the first ledger server an internal timestamp and aninternal signature for the most recent timestamp block storing the firsttimestamp and associated signature.

After receiving the first timestamp and associated signature from thecentralized ledger server, the first ledger server can store the firsttimestamp and associated signature in the first blockchain. In someembodiments, the first block is a most current block to be generated inthe first blockchain when the first ledger server transmits the firsttimestamp request to the centralized ledger server. The first timestamprequest can include a hash of transaction data to be stored in the firstblock. After receiving the first timestamp and associated signature, thefirst ledger server can generate the most current block including thefirst timestamp and associated signature as a transaction and thetransaction data for the first block.

In some embodiments, the first block is a most recent generated block inthe first blockchain when the first ledger server transmits the firsttimestamp request to the centralized ledger server. The first timestamprequest can include a hash of the first block. After receiving the firsttimestamp and associated signature, the ledger server can store thefirst timestamp and associated signature as a transaction in a secondblock immediately subsequent to the first block in the first blockchain.The second block can also store the hash of the first block. In someembodiments, the second block can store the first timestamp andassociated signature together with transaction data for the secondblock. In some embodiments, the second block can be a block whose blockbody exclusively includes the first timestamp and associated signaturewithout storing other transaction data.

FIG. 7 depicts examples of modules of an apparatus 700 in accordancewith embodiments of this specification. The apparatus 700 can be anexample of an embodiment of a blockchain-based centralized ledger systemconfigured to provide ledger services and/or trust timestamp servicesfor transaction data stored in the centralized ledger system. Theapparatus 700 can correspond to the embodiments described above, and theapparatus 700 includes the following: a first receiving module 702 thatreceives timestamps and associated signatures from a trust time serverthat is associated with a trust time authority and independent from theblockchain-based centralized ledger system; a storing module 704 thatstores the timestamps and associated signatures of the trust time serverin a centralized timestamp blockchain, the centralized trust timestampblockchain including a plurality of timestamp blocks storing trusttimestamp information of the trust time server for the blockchain-basedcentralized ledger system that stores data in a plurality ofblockchains, each of the plurality of blockchains including a pluralityof blocks storing transaction data; a second receiving module 706 thatreceives a first timestamp request for a first block of a firstblockchain from a first ledger server; and a transmitting module 708that transmits a first timestamp and associated signature that is storedin the timestamp blockchain and corresponds to the first timestamprequest to the first ledger server.

In an optional embodiment, the first block is a most current block to begenerated in the first blockchain when the first timestamp request istransmitted by the first ledger server, and the first timestamp requestincludes a hash of transaction data to be stored in the first block.

In an optional embodiment, the first ledger server includes a generatingmodule that generates the first block storing the first timestamp andthe associated signature as a transaction and the transaction data bythe first ledger server.

In an optional embodiment, the first block is a most recent blockgenerated in the first blockchain when the first timestamp request istransmitted by the first ledger server, and the first timestamp requestincludes a hash of the first block.

In an optional embodiment, the first ledger server includes a storingmodule that stores the first timestamp and the associated signature as atransaction in a second block immediately subsequent to the first blockin the first blockchain by the first ledger server. The second block canstore the hash of the first block.

In an optional embodiment, the apparatus 700 further includes a secondtransmitting module that periodically transmits server timestamprequests to the trust time server.

In an optional embodiment, each of the server timestamp requestsincludes at least one of: an identifier of the server timestamp requestamong the server timestamp requests, an identifier of a most currenttimestamp block to be generated in the centralized trust timestampblockchain, or at least one of an identifier or a hash of a most recenttimestamp block generated in the centralized trust timestamp blockchain.

In an optional embodiment, the storing module 704 is configured to: inresponse to receiving a particular timestamp and associated signaturefrom the trust time server, generate a particular timestamp block in thecentralized trust timestamp blockchain, the particular timestamp blockincluding the particular timestamp and the associated signature as atransaction.

In an optional embodiment, the first timestamp and the associatedsignature are stored in a most recent timestamp block generated in thecentralized trust timestamp blockchain when the first timestamp requestis received.

In an optional embodiment, the apparatus 700 includes a generatingmodule that generates an internal timestamp signature for the mostrecent timestamp block storing the first timestamp and associatedsignature and an internal signature encrypting the internal timestampand the most recent timestamp block. The transmitting module 708 can beconfigured to transmit the internal timestamp and the internalsignature, together with the first timestamp and associated signature,to the first ledger server.

In an optional embodiment, the first ledger server is configured toperiodically transmit timestamp requests for blocks in the firstblockchain to the centralized ledger server.

In an optional embodiment, the second receiving module 706 is configuredto receive a second timestamp request from a second ledger serverassociated with a second blockchain different from the first blockchain,and the transmitting module 708 is configured to transmit a secondtimestamp and associated signature that is stored in the timestampblockchain and corresponds to the second timestamp request to the secondledger server.

In an optional embodiment, each of ledger servers in the centralizedledger system is configured to maintain a plurality of blockchains eachincluding a plurality of blocks storing transaction data.

In an optional embodiment, the apparatus 700 further includes amaintaining module that maintains the centralized trust timestampblockchain by sequentially storing timestamps and associated signaturesin respective timestamp blocks according to a chronological order ofreceiving the timestamps and associated signatures from the trust timeserver. The blockchain-based centralized ledger system maintains theplurality of blockchains by a plurality corresponding ledger servers.

The system, apparatus, module, or unit illustrated in the previousembodiments can be implemented by using a computer chip or an entity, orcan be implemented by using a product having a certain function. Atypical embodiment device is a computer (and the computer can be apersonal computer), a laptop computer, a cellular phone, a camera phone,a smartphone, a personal digital assistant, a media player, a navigationdevice, an email receiving and sending device, a game console, a tabletcomputer, a wearable device, or any combination of these devices.

For an embodiment process of functions and roles of each module in theapparatus, references can be made to an embodiment process ofcorresponding steps in the previous method. Details are omitted here forsimplicity.

Because an apparatus embodiment basically corresponds to a methodembodiment, for related parts, references can be made to relateddescriptions in the method embodiment. The previously describedapparatus embodiment is merely an example. The modules described asseparate parts may or may not be physically separate, and partsdisplayed as modules may or may not be physical modules, may be locatedin one position, or may be distributed on a number of network modules.Some or all of the modules can be selected based on actual demands toachieve the objectives of the solutions of the specification. A personof ordinary skill in the art can understand and implement theembodiments of the present application without creative efforts.

Referring again to FIG. 7, it can be interpreted as illustrating aninternal functional module and a structure of a blockchain-basedcentralized ledger implementation apparatus. The blockchain-basedcentralized ledger implementation apparatus can be an example of acentralized ledger system configured to provide ledger services andtrust timestamp services for transaction data stored in the centralizedledger system. An execution body in essence can be an electronic device,and the electronic device includes the following: one or moreprocessors; and one or more computer-readable memories configured tostore an executable instruction of the one or more processors. In someembodiments, the one or more computer-readable memories are coupled tothe one or more processors and have programming instructions storedthereon that are executable by the one or more processors to performalgorithms, methods, functions, processes, flows, and procedures, asdescribed in this specification.

Described embodiments of the subject matter can include one or morefeatures, alone or in combination. For example, in a first embodiment, amethod includes: receiving timestamps and associated signatures from atrust time server by a centralized ledger server in the blockchain-basedcentralized ledger system, the trust time server being associated with atrust time authority and independent from the blockchain-basedcentralized ledger system; storing the timestamps and the associatedsignatures of the trust time server in the centralized trust timestampblockchain by the centralized ledger server, the centralized trusttimestamp blockchain including a plurality of timestamp blocks storingtrust timestamp information of the trust time server for ablockchain-based centralized ledger system that stores data in aplurality of blockchains, each of the plurality of blockchains includinga plurality of blocks storing transaction data; receiving a firsttimestamp request for a first block of a first blockchain from a firstledger server associated with the first blockchain by the centralizedledger server; and transmitting a first timestamp and associatedsignature that is stored in the timestamp blockchain and corresponds tothe first timestamp request to the first ledger server by thecentralized ledger server.

The foregoing and other described embodiments can each, optionally,include one or more of the following features:

A first feature, combinable with any of the following features,specifies that the first block is a most current block to be generatedin the first blockchain when the first timestamp request is transmittedby the first ledger server, and the first timestamp request includes ahash of transaction data to be stored in the first block.

A second feature, combinable with any of the previous or followingfeatures, specifies that the first ledger server is configured togenerate the first block storing the first timestamp and the associatedsignature as a transaction and the transaction data.

A third feature, combinable with any of the previous or followingfeatures, specifies that the first block is a most recent blockgenerated in the first blockchain when the first timestamp request istransmitted by the first ledger server, and the first timestamp requestincludes a hash of the first block.

A fourth feature, combinable with any of the previous or followingfeatures, specifies that the first ledger server is configured to storethe first timestamp and the associated signature as a transaction in asecond block immediately subsequent to the first block in the firstblockchain, and the second block stores the hash of the first block.

A fifth feature, combinable with any of the previous or followingfeatures, further includes: periodically transmitting server timestamprequests to the trust time server by the centralized ledger server.

A sixth feature, combinable with any of the previous or followingfeatures, specifies that each of the server timestamp requests comprisesat least one of: an identifier of the server timestamp request among theserver timestamp requests, an identifier of a most current timestampblock to be generated in the centralized trust timestamp blockchain, orat least one of an identifier or a hash of a most recent timestamp blockgenerated in the centralized trust timestamp blockchain.

A seventh feature, combinable with any of the previous or followingfeatures, specifies that storing the timestamps and the associatedsignatures of the trust time server in a centralized trust timestampblockchain includes: in response to receiving a particular timestamp andassociated signature from the trust time server, generating a particulartimestamp block in the centralized trust timestamp blockchain, theparticular timestamp block including the particular timestamp and theassociated signature as a transaction.

An eight feature, combinable with any of the previous or followingfeatures, specifies that the first timestamp and the associatedsignature are stored in a most recent timestamp block generated in thecentralized trust timestamp blockchain when the first timestamp requestis received.

A ninth feature, combinable with any of the previous or followingfeatures, further includes: generating an internal timestamp signaturefor the most recent timestamp block storing the first timestamp andassociated signature by the centralized ledger server; generating aninternal signature encrypting the internal timestamp and the most recenttimestamp block by the centralized ledger server; and transmitting theinternal timestamp and the internal signature, together with the firsttimestamp and associated signature, to the first ledger server by thecentralized ledger server.

A tenth feature, combinable with any of the previous or followingfeatures, specifies that the first ledger server is configured toperiodically transmit timestamp requests for blocks in the firstblockchain to the centralized ledger server.

An eleventh feature, combinable with any of the previous or followingfeatures, further includes: receiving a second timestamp request from asecond ledger server associated with a second blockchain different fromthe first blockchain by the centralized ledger server; and transmittinga second timestamp and associated signature that is stored in thetimestamp blockchain and corresponds to the second timestamp request tothe second ledger server by the centralized ledger server.

A twelfth feature, combinable with any of the previous or followingfeatures, further includes: maintaining a plurality of blockchains bycorresponding ledger servers in the centralized ledger system andmaintaining the centralized trust timestamp blockchain by thecentralized ledger server, where the centralized ledger server isconfigured to sequentially store timestamps and associated signatures ofthe trust time server in respective timestamp blocks according to achronological order of receiving the timestamps and associatedsignatures from the trust time server.

Embodiments of the subject matter and the actions and operationsdescribed in this specification can be implemented in digital electroniccircuitry, in tangibly-embodied computer software or firmware, incomputer hardware, including the structures disclosed in thisspecification and their structural equivalents, or in combinations ofone or more of them. Embodiments of the subject matter described in thisspecification can be implemented as one or more computer programs, e.g.,one or more modules of computer program instructions, encoded on acomputer program carrier, for execution by, or to control the operationof, data processing apparatus. For example, a computer program carriercan include one or more computer-readable storage media that haveinstructions encoded or stored thereon. The carrier may be a tangiblenon-transitory computer-readable medium, such as a magnetic, magnetooptical, or optical disk, a solid state drive, a random access memory(RAM), a read-only memory (ROM), or other types of media. Alternatively,or in addition, the carrier may be an artificially generated propagatedsignal, e.g., a machine-generated electrical, optical, orelectromagnetic signal that is generated to encode information fortransmission to suitable receiver apparatus for execution by a dataprocessing apparatus. The computer storage medium can be or be part of amachine-readable storage device, a machine-readable storage substrate, arandom or serial access memory device, or a combination of one or moreof them. A computer storage medium is not a propagated signal.

A computer program, which may also be referred to or described as aprogram, software, a software application, an app, a module, a softwaremodule, an engine, a script, or code, can be written in any form ofprogramming language, including compiled or interpreted languages, ordeclarative or procedural languages; and it can be deployed in any form,including as a stand-alone program or as a module, component, engine,subroutine, or other unit suitable for executing in a computingenvironment, which environment may include one or more computersinterconnected by a data communication network in one or more locations.

A computer program may, but need not, correspond to a file in a filesystem. A computer program can be stored in a portion of a file thatholds other programs or data, e.g., one or more scripts stored in amarkup language document, in a single file dedicated to the program inquestion, or in multiple coordinated files, e.g., files that store oneor more modules, sub programs, or portions of code.

Processors for execution of a computer program include, by way ofexample, both general- and special-purpose microprocessors, and any oneor more processors of any kind of digital computer. Generally, aprocessor will receive the instructions of the computer program forexecution as well as data from a non-transitory computer-readable mediumcoupled to the processor.

The term “data processing apparatus” encompasses all kinds ofapparatuses, devices, and machines for processing data, including by wayof example a programmable processor, a computer, or multiple processorsor computers. Data processing apparatus can include special-purposelogic circuitry, e.g., an FPGA (field programmable gate array), an ASIC(application specific integrated circuit), or a GPU (graphics processingunit). The apparatus can also include, in addition to hardware, codethat creates an execution environment for computer programs, e.g., codethat constitutes processor firmware, a protocol stack, a databasemanagement system, an operating system, or a combination of one or moreof them.

The processes and logic flows described in this specification can beperformed by one or more computers or processors executing one or morecomputer programs to perform operations by operating on input data andgenerating output. The processes and logic flows can also be performedby special-purpose logic circuitry, e.g., an FPGA, an ASIC, or a GPU, orby a combination of special-purpose logic circuitry and one or moreprogrammed computers.

Computers suitable for the execution of a computer program can be basedon general or special-purpose microprocessors or both, or any other kindof central processing unit. Generally, a central processing unit willreceive instructions and data from a read only memory or a random accessmemory or both. Elements of a computer can include a central processingunit for executing instructions and one or more memory devices forstoring instructions and data. The central processing unit and thememory can be supplemented by, or incorporated in, special-purpose logiccircuitry.

Generally, a computer will also include, or be operatively coupled toreceive data from or transfer data to one or more storage devices. Thestorage devices can be, for example, magnetic, magneto optical, oroptical disks, solid state drives, or any other type of non-transitory,computer-readable media. However, a computer need not have such devices.Thus, a computer may be coupled to one or more storage devices, such as,one or more memories, that are local and/or remote. For example, acomputer can include one or more local memories that are integralcomponents of the computer, or the computer can be coupled to one ormore remote memories that are in a cloud network. Moreover, a computercan be embedded in another device, e.g., a mobile telephone, a personaldigital assistant (PDA), a mobile audio or video player, a game console,a Global Positioning System (GPS) receiver, or a portable storagedevice, e.g., a universal serial bus (USB) flash drive, to name just afew.

Components can be “coupled to” each other by being commutatively such aselectrically or optically connected to one another, either directly orvia one or more intermediate components. Components can also be “coupledto” each other if one of the components is integrated into the other.For example, a storage component that is integrated into a processor(e.g., an L2 cache component) is “coupled to” the processor.

To provide for interaction with a user, embodiments of the subjectmatter described in this specification can be implemented on, orconfigured to communicate with, a computer having a display device,e.g., a LCD (liquid crystal display) monitor, for displaying informationto the user, and an input device by which the user can provide input tothe computer, e.g., a keyboard and a pointing device, e.g., a mouse, atrackball or touchpad. Other kinds of devices can be used to provide forinteraction with a user as well; for example, feedback provided to theuser can be any form of sensory feedback, e.g., visual feedback,auditory feedback, or tactile feedback; and input from the user can bereceived in any form, including acoustic, speech, or tactile input. Inaddition, a computer can interact with a user by sending documents toand receiving documents from a device that is used by the user; forexample, by sending web pages to a web browser on a user's device inresponse to requests received from the web browser, or by interactingwith an app running on a user device, e.g., a smartphone or electronictablet. Also, a computer can interact with a user by sending textmessages or other forms of message to a personal device, e.g., asmartphone that is running a messaging application, and receivingresponsive messages from the user in return.

This specification uses the term “configured to” in connection withsystems, apparatus, and computer program components. For a system of oneor more computers to be configured to perform particular operations oractions means that the system has installed on it software, firmware,hardware, or a combination of them that in operation cause the system toperform the operations or actions. For one or more computer programs tobe configured to perform particular operations or actions means that theone or more programs include instructions that, when executed by dataprocessing apparatus, cause the apparatus to perform the operations oractions. For special-purpose logic circuitry to be configured to performparticular operations or actions means that the circuitry has electroniclogic that performs the operations or actions.

While this specification contains many specific embodiment details,these should not be construed as limitations on the scope of what isbeing claimed, which is defined by the claims themselves, but rather asdescriptions of features that may be specific to particular embodiments.Certain features that are described in this specification in the contextof separate embodiments can also be realized in combination in a singleembodiment. Conversely, various features that are described in thecontext of a single embodiments can also be realized in multipleembodiments separately or in any suitable subcombination. Moreover,although features may be described above as acting in certaincombinations and even initially be claimed as such, one or more featuresfrom a claimed combination can in some cases be excised from thecombination, and the claim may be directed to a subcombination orvariation of a subcombination.

Similarly, while operations are depicted in the drawings and recited inthe claims in a particular order, this should not be understood asrequiring that such operations be performed in the particular ordershown or in sequential order, or that all illustrated operations beperformed, to achieve desirable results. In certain circumstances,multitasking and parallel processing may be advantageous. Moreover, theseparation of various system modules and components in the embodimentsdescribed above should not be understood as requiring such separation inall embodiments, and it should be understood that the described programcomponents and systems can generally be integrated together in a singlesoftware product or packaged into multiple software products.

Particular embodiments of the subject matter have been described. Otherembodiments are within the scope of the following claims. For example,the actions recited in the claims can be performed in a different orderand still achieve desirable results. As one example, the processesdepicted in the accompanying figures do not necessarily require theparticular order shown, or sequential order, to achieve desirableresults. In some cases, multitasking and parallel processing may beadvantageous.

1-30. (canceled)
 31. A computer-implemented method for managing a blockchain-based centralized ledger system, the computer-implemented method comprising: maintaining a centralized trust timestamp blockchain by a centralized ledger server in the centralized ledger system, the centralized ledger server comprising a plurality of timestamp blocks, each of the plurality of timestamp blocks storing a respective trust timestamp and associated signature from a trust time server, the trust time server being associated with a trust time authority and independent from the centralized ledger system; receiving a first timestamp request for a first data block of a data blockchain from a ledger server associated with the data blockchain by the centralized ledger server, the data blockchain comprising a plurality of data blocks storing transaction data; and transmitting a first timestamp and associated signature that is stored in the centralized trust timestamp blockchain and corresponds to the first timestamp request to the ledger server by the centralized ledger server.
 32. The computer-implemented method of claim 31, wherein the first data block is a most current data block to be generated in the data blockchain when the first timestamp request is transmitted by the ledger server, and wherein the first timestamp request comprises a hash of first transaction data to be stored in the first data block.
 33. The computer-implemented method of claim 32, wherein the first data block stores the first timestamp and associated signature as a transaction and the first transaction data.
 34. The computer-implemented method of claim 31, wherein the first data block is a most recent data block generated in the data blockchain when the first timestamp request is transmitted by the ledger server, and wherein the first timestamp request comprises a hash of the first data block.
 35. The computer-implemented method of claim 34, wherein the first timestamp and associated signature is stored as a transaction in a first timestamped block immediately subsequent to the first data block in the data blockchain, wherein the first timestamped block stores the hash of the first data block.
 36. The computer-implemented method of claim 31, wherein the first timestamp and associated signature is stored in a most recent timestamp block generated in the centralized trust timestamp blockchain when the first timestamp request is received.
 37. The computer-implemented method of claim 36, further comprising: generating an internal timestamp for the most recent timestamp block storing the first timestamp and associated signature by the centralized ledger server; generating an internal signature encrypting the internal timestamp and the most recent timestamp block by the centralized ledger server; and transmitting the internal timestamp and the internal signature, together with the first timestamp and associated signature, to the ledger server by the centralized ledger server.
 38. The computer-implemented method of claim 31, further comprising: periodically receiving timestamp requests for data blocks in the data blockchain from the ledger server by the centralized ledger server.
 39. The computer-implemented method of claim 31, wherein the data blockchain comprises a plurality of timestamped blocks each storing respective timestamps and associated signatures from the centralized trust timestamp blockchain, any adjacent two of the timestamped blocks in the data blockchain being anchored with each other.
 40. The computer-implemented method of claim 31, further comprising: receiving a second timestamp request from a second ledger server associated with a second data blockchain by the centralized ledger server; and transmitting a second timestamp and associated signature that is stored in the centralized trust timestamp blockchain and corresponds to the second timestamp request to the second ledger server by the centralized ledger server.
 41. A non-transitory, computer-readable medium storing one or more instructions executable by a computer-implemented system to perform operations for managing a blockchain-based centralized ledger system, the operations comprising: maintaining a centralized trust timestamp blockchain that comprises a plurality of timestamp blocks, each of the plurality of timestamp blocks storing a respective trust timestamp and associated signature from a trust time server, the trust time server being associated with a trust time authority and independent from the centralized ledger system; receiving a first timestamp request for a first data block of a data blockchain from a ledger server associated with the data blockchain, the data blockchain comprising a plurality of data blocks storing transaction data; and transmitting a first timestamp and associated signature that is stored in a centralized trust timestamp blockchain and corresponds to the first timestamp request to the ledger server.
 42. The non-transitory, computer-readable medium 41, wherein the first data block is a most current data block to be generated in the data blockchain when the first timestamp request is transmitted by the ledger server, and wherein the first timestamp request comprises a hash of first transaction data to be stored in the first data block.
 43. The non-transitory, computer-readable medium 42, wherein the first data block stores the first timestamp and associated signature as a transaction and the first transaction data.
 44. The non-transitory, computer-readable medium 41, wherein the first data block is a most recent data block generated in the data blockchain when the first timestamp request is transmitted by the ledger server, wherein the first timestamp request comprises a hash of the first data block, and wherein the first timestamp and associated signature is stored as a transaction in a first timestamped block immediately subsequent to the first data block in the data blockchain, wherein the first timestamped block stores the hash of the first data block.
 45. The non-transitory, computer-readable medium 41, wherein the first timestamp and associated signature is stored in a most recent timestamp block generated in the centralized trust timestamp blockchain when the first timestamp request is received.
 46. The non-transitory, computer-readable medium 45, wherein the operations further comprise: generating an internal timestamp for the most recent timestamp block storing the first timestamp and associated signature; generating an internal signature encrypting the internal timestamp and the most recent timestamp block; and transmitting the internal timestamp and the internal signature, together with the first timestamp and associated signature, to the ledger server.
 47. The non-transitory, computer-readable medium 41, wherein the operations further comprise: periodically receiving timestamp requests for data blocks in the data blockchain from the ledger server.
 48. The non-transitory, computer-readable medium 41, wherein the data blockchain comprises a plurality of timestamped blocks each storing respective timestamps and associated signatures from the centralized trust timestamp blockchain, any adjacent two of the timestamped blocks in the data blockchain being anchored with each other.
 49. The non-transitory, computer-readable medium 41, wherein the operations further comprise: receiving a second timestamp request from a second ledger server associated with a second data blockchain; and transmitting a second timestamp and associated signature that is stored in the centralized trust timestamp blockchain and corresponds to the second timestamp request to the second ledger server.
 50. A computer-implemented system, comprising: one or more processors; and one or more non-transitory machine readable storage medium coupled to the one or more processors and having machine-executable instructions stored thereon that, when executed by the one or more processors, cause the one or more processors to perform operations for managing a blockchain-based centralized ledger system, the operations comprising: maintaining a centralized trust timestamp blockchain that comprises a plurality of timestamp blocks, each of the plurality of timestamp blocks storing a respective trust timestamp and associated signature from a trust time server, the trust time server being associated with a trust time authority and independent from the centralized ledger system; receiving a timestamp request for a data block of a data blockchain from a ledger server associated with the data blockchain, the data blockchain comprising a plurality of data blocks storing transaction data; and transmitting a timestamp and associated signature that is stored in a centralized trust timestamp blockchain and corresponds to the timestamp request to the ledger server. 